1. Field of the Invention
The present invention relates to a forebody flow control system and more particularly to aircraft or missile flow control system for enhanced maneuverability and stabilization, particularly at high angles of attack. The present invention further relates to a method of operating the flow control system.
2. Technical Background
In numerous aeronautical applications it is desirable to control the flow across a surface. As fluid flows over a surface, like air over an aircraft or a missile forebody, it forms a fluid boundary layer at the surface. The fluid boundary layer is a thin layer of viscous flow exhibiting certain pressure variations that affect the operation of the aircraft or a missile.
One of these variations is the separation and vortex induced phantom yaw caused by asymmetric vortex shedding on an aircraft or a missile at high angles of attack, even at zero angle of sideslip. Large forces and dynamic out-of-plane loading on the aircraft or missile occur at angles of attack ranging from 30 to 60 degrees. It is known that the out-of-plane loading results from micro-asymmetries on the surface of the nose of the aircraft or missile such as dents, cracks in the paint and other microscopic imperfections near the tip of the nose. It has also been known that these asymmetries are affected by the bluntness of the forebody, Reynolds Number; roll angle, and the angle of attack. At high angles of attack, these side forces (yaw) are especially pronounced due to ineffectiveness of the traditional flight control surfaces. Side forces resulting from these asymmetries adversely affect the missile or aircraft's performance and significantly limit their flight envelope.
The demand for better control of missiles or aircraft at high angles of attack has led to a number of approaches for control of these side forces. Flow control devices have been employed to control and counteract these side forces. These flow control devices are either passive or active. Passive flow control devices have included geometric changes to the forebody structure such as nose bluntness, strakes, boundary layer strips, vane vortex generators and rotating nose tips to control the asymmetric vortices off the forebody. These passive flow control techniques are effective to some extent in alleviating these side forces, but at the same time limit the performance of the aircraft or missile by increasing the drag. Active flow control devices have included jet blowing, unsteady bleed, suction, blowing and deployable flow effectors to control the asymmetric vortices off the fore body. These active flow control techniques are (as with passive devices) also effective to some extent in alleviating these side forces, but also not optimized (as with passive devices), because they operate in an open-loop mode with no sensor feedback, at the same time limit the performance of the aircraft or missile by increasing the drag.
In view of the foregoing disadvantages with presently available passive or active flow control systems and methods for controlling flow asymmetries on a missile or an aircraft, it has become desirable to develop a missile or aircraft forebody flow control system that controls both the magnitude and direction of these side forces (and further the aircraft or missile maneuverability), and can be deactivated when not required in order to reduce drag.